Optical monitoring of one or more optical signals is desirable in many applications. In general, a fraction of an optical signal is sampled by using a power splitter (tap) to out-couple a small portion of a propagating optical signal and direct this small portion into an optical detector to determine the power level (and/or other information) of the signal. The monitor power may be only a small fraction of the signal so that the measurement does not significantly affect the power level of the primary signal. Such optical monitoring may be implemented in fiber communication networks to monitor optical signals at selected locations.
Additionally, there are various types of “active” optical system components that need to be adjusted/tuned to meet certain operational requirements. For example, in multi-wavelength optical communication systems, it may be desirable to maintain an essentially uniform power level output signal at each wavelength. In fiber-based optical amplifiers utilizing multiple wavelengths, there is often a desire to maintain a particular gain distribution (including “flat”) across the wavelength spectrum. These situations are considered to be exemplary only; there are various instances where it is desirable (if not necessary) to monitor optical signal power levels.
Typical configurations of optical tap monitors consist of at least three discrete components: a dual-fiber collimator, a highly-reflective dielectric mirror, and a photodetector disposed behind the mirror. FIG. 1 is a simplified diagram of this prior art configuration, illustrating a collimator 1, dielectric mirror 2 and photodetector 3. In operation, an optical signal propagating along an input fiber 4 passes through collimator 1 and dielectric mirror 2. The composition and thickness of dielectric mirror 2 is designed such that only a relatively small portion of the signal will be transmitted through dielectric mirror 2 to impinge photodetector 3, with the majority of the signal reflected by mirror 2. The reflected signal will again pass through collimator 1 and then be coupled into an output fiber 5. Photodetector 3 functions to convert the small transmitted portion of the optical signal into an electrical equivalent which can be further processed to provide a measurement of the optical power in this signal. The measured output from photodetector 3 may be used to assess the performance of the optical system in terms of the power present in the optical signal.
Conventional prior art designs of tap monitors include the following elements: (1) a 1×2 fused optical coupler designed to exhibit an X%/(100−X)% splitting ratio (e.g., 5%/95%), (2) a discrete element photodetector; and (3) a fiber splice that connects the low power output of the coupler to the photodetector. While this approach is relatively simple to implement, there is a need to perform alignments between the discrete components as the monitor is being assembled, as well as after the monitor is in place. Additionally, its use of discrete components means that the overall size of the tap monitor may be significant, and the included fiber splices need to be carefully formed and managed.